fsnotify: Panic on Mac OS X when debugging

Before reporting an issue, please ensure you are using the latest release of fsnotify.

Which operating system (GOOS) and version are you using?

OS: ProductName: Mac OS X ProductVersion: 10.12.5 BuildVersion: 16F73

Go: go version go1.8.3 darwin/amd64

Delve: Delve Debugger Version: 1.0.0-rc.1 Build:

IDE: Visual Studio Code Ver 1.14.1 (1.14.1) 2648980a697a4c8fb5777dcfb2ab110cec8a2f58 2017-07-13T19:05:02.227Z

Please describe the issue that occurred.

When execution continues after stop at breakpoint then panic raised at kqueue.go -> read(kq int, events []unix.Kevent_t, timeout *unix.Timespec)

Are you able to reproduce the issue? Please provide steps to reproduce and a code sample if possible.

I use sample code from https://github.com/fsnotify/fsnotify/blob/master/example_test.go
Set up breakpoint at any place
Trigger breakpoint
When step over or continue execution then panic raised

panic: runtime error: slice bounds out of range

goroutine 8 [running]:
bitbucket.org/project/vendor/github.com/fsnotify/fsnotify.read(0x8, 0xc4202e0e88, 0xa, 0xa, 0x1708c50, 0xc4202e0e88, 0x0, 0xa, 0x0, 0x0)

/path_to_project/vendor/github.com/fsnotify/fsnotify/kqueue.go:498 +0x2fe
bitbucket.org/litkiosk/litkiosk_server/vendor/github.com/fsnotify/fsnotify.(*Watcher).readEvents(0xc42001c360)

/path_to_project/vendor/github.com/fsnotify/fsnotify/kqueue.go:284 +0xda
created by bitbucket.org/litkiosk/litkiosk_server/vendor/github.com/fsnotify/fsnotify.NewWatcher

/path_to_project/vendor/github.com/fsnotify/fsnotify/kqueue.go:62 +0x2c8

I added log in this function

func read(kq int, events []unix.Kevent_t, timeout *unix.Timespec) ([]unix.Kevent_t, error) {
	n, err := unix.Kevent(kq, nil, events, timeout)
	if err != nil {
		return nil, err
	}
	fmt.Println("n", n, "len", len(events), "cap", cap(events))
	return events[0:n], nil
}

and it prints

n 0 len 10 cap 10
n 0 len 10 cap 10
n 0 len 10 cap 10
n 0 len 10 cap 10
2017/07/15 12:00:40 debugger.go:505: continuing
n 33554795 len 10 cap 10

About this issue

Original URL
State: closed
Created 7 years ago
Reactions: 22
Comments: 18 (2 by maintainers)

Commits related to this issue

Temporary fix for osx debug panic https://github.com/fsnotify/fsnotify/issues/212#issuecomment-360862770 — committed to nwingert/fsnotify by nwingert 6 years ago

Most upvoted comments

I have been able to work around the panic by making the following modification in kqueue.go:

func min(x, y int) int {
	if x < y {
		return x
	}
	return y
}

// read retrieves pending events, or waits until an event occurs.
// A timeout of nil blocks indefinitely, while 0 polls the queue.
func read(kq int, events []unix.Kevent_t, timeout *unix.Timespec) ([]unix.Kevent_t, error) {
	n, err := unix.Kevent(kq, nil, events, timeout)
	if err != nil {
		return nil, err
	}
	n = min(n, len(events) - 1)   // new
	return events[0:n], nil
}

joatmon on Jan 26, 2018

+1 I have added some code to avoid this issue on my local machine

kquene.go

func read(kq int, events []unix.Kevent_t, timeout *unix.Timespec) ([]unix.Kevent_t, error) {
	n, err := unix.Kevent(kq, nil, events, timeout)
	if err != nil {
		return nil, err
	}
+	if len(events) < n {
+		n = 0
+	}
	return events[0:n], nil
}

vinkdong on Dec 19, 2018

Same issue with GoLand and https://www.jetbrains.com/go/

vyarmak on Oct 13, 2022